Final Exam Flashcards
What is isostasy?
The reason that continents can rise above oceans. Buoyant continental lithosphere floats on dense asthenosphere; lithosphere can thicken, forming higher mountains and correspondingly deeper roots.
Which is heavier, lithosphere or asthenosphere?
Asthenosphere, lithosphere floats on top of it and is buoyant
What are mountain building processes collectively called?
Orogenesis
What kind of belts do mountains form?
Orogenic belts
What do orogenic belts parallel?
Continental margins
How does an orogenic belt parallel a divergent margin?
At a divergent boundary, the mantle plume rises, uplifts, and splits continental lithosphere forming rift valleys with blocks dropped along normal faults, and volcanoes along valley sides
How does an orogenic belt parallel a passive margin?
A rift widens, filling with seawater forming a new ocean basin - the sides of the ocean basin experience no seismic activity but gradually subside under the weight of the sediment load
How does an orogenic belt parallel a convergent margin?
As mountains grow at converget boundaries, they undergo isostatic adjustments which balance their weight
When do the highest mountains form?
At continental collisions
What is an Andean type convergent boundary?
Denser oceanic lithosphere subducts beneath continental lithosphere, developing into an accretionary wedge, a continental volcanic arc, and plutons form in the middle of deformed mountains (andesitic and granitic)
Which type of margin has no seismic activity?
A passive boundary
Which type of margin forms a continental volcanic arc?
An andean-type, converging margin
What is an accretionary wedge?
Plastered against the edge of the continental lithosphere, it undergoes metamorphosis
What is an Alleution-type convergent boundary?
Occurs when oceanic lithosphere subducts under more oceanic lithosphere: forms an oceanic-oceanic volcanic island arc.
Which type of margin forms a volcanic island arc?
A convergent Alleutian-type boundary
What occurs in a convergent, continental collision?
An ocean basin closes, subduction stops, and the highest mountains can form. The “suture” is place where the two plates collide. There is no volcanic activity that occurs here.
What is a convergent, accreted terrane?
Occurs when a foreign piece of crust forcefully attaches to a continental margin (ex. transportation of an island across an ocean). Transportation due to sea floor spreading.
What is the Wilson Cycle?
When the ocean opens and then closes again. Mountains are builts, and then rebuilt repeatedly, rarely, pieces of the ocean floor are scraped up and elevated with the mountain belt in the form of obduction.
What is obduction?
When pieces of the oceanic floor got “stuck” on top of continental margins in the Wilson cycle.
What are broad, vertical movements in continents?
More than just isostatic adjustments alone
What is uplift, as a vertical, continent movement?
Due to mantle upwelling that pushes up continental lithosphere in the interior of a continent
What is subsidence, as a broad, vertical movement in a continent?
Subsidence is due to the weight of sediment deposited along passive continental margins as a mountain belt erodes, as well as downward mantle flow pulling on the lithosphere.
Where is subsidence likely to occur?
At a passive continental margin where mountain belts are eroding to form sediments.
How did continental crust originally form?
Originally, by the accretion of mantle material. Oceanic crust was subducted below continental crust. Magma differentiated to produce andesitic and granitic volcanic arcs that coalesced to form Earth’s earliest crude continents
What was the last supercontinent that was broken up?
Pangaea
Where are the earliest rocks found? What do they look like?
Found in shield areas of continental crust. They are highly deformed and metamorphosed, representing multiple cycles of orogenesis and the break-up of supercontinents.
What are the controls and triggers for mass wasting?
- Gravity
- Oversteepened slopes
- Vegetation (or lack there of)
- Earthquakes
How does gravity impact mass wasting?
Gravity is important, but gravity and water is critical. When water completely fills pores it reduces cohesion and allows grains to slide over each other, while adding weight to the soil
How does water impact mass wasting?
When water completely fills pores, it
a) Reduces cohesion between particles (reduces friction)
b) Adds weight to the soil
How does oversteepening of slopes cause mass wasting? How does it occur?
It causes loss of support for materials higher up the slope. It occurs by undercutting waves, undercutting streams, and human excavation.
How does vegetation impact mass wasting?
Vegetation is anchored into the soil by roots which keeps the soil and regolith in place. Removing plants makes the slope unstable and susceptible to failure.
How do earthquakes impact mass wasting?
Earthquakes can dislodge rock and unconsolidated material, resulting in landslides on slopes
How are different types of mass wasting classified?
- The types of materials
- How fast they move
- The type of motion (free falling, flowing, sliding)
What is a slump?
Type of material: rock and unconsolidated material commonly lubricated by water
Movement: moves as blocks along curved surfaces in a rotational way way, away from a scarp with the block’s surface tilting back
When it happens: when the slope is undercut by stream, waves, or human excavation
What is a rock slide?
Commonly occurs if a slope is cut by a stream, after heavy rain or snow melt, or after an earthquake, in mountainous areas. Occurs where strata or a joint parallels the slope, or where stronger rocks overlie weaker ones.
Some travel up to 200 km/h!
This mass wasting process may result in rock travelling up to 200 km/h!
Rock slide
Debris flow
Mixture of water-saturated soil and regolith that moves rapidly down canyons and stream channels of semi-arid mountainous regions. Occurs following heavy rainflow.
Also, volcanic lahars of wet and muddy ash rushing dow valleys.
Where does debris flow usually occur?
Semi-arid mountainsides, canyons, and stream channels and near volcanoes after rainflow
What is earthflow?
Commonly begins as a slump. Very slow and ongoing movement (may occur for years) of mud down hillsides in humid areas.
Forms a tongue-shaped mass that may move for years.
Forms a tongue-shaped mass that may move for years
Earthflow
Mass wasting that commonly begins as slump.
Earthflow
What is creep?
The gradual, downslope movement of soil and regolith under gravity; caused by repeated freezing and thawing or wetting and drying.
Results in tilted trees, fences, utility poles, etc.
Causes the tilting of utility poles/trees.
Creep
What is the mass wasting process of solifluction?
Flow that occurs on saturated ground, overlaying impermeable rock such clay, or permafrost in polar areas. Water cannot percolate downwards on the surface, so material moves slowly downwards as lobes.
What is a submarine landslide?
Occurs as slumps under water, with debris flow and turbidity currents.
What percentage of the water on earth is stored in the ocean?
97%
What occurs during the hydrological cycle?
97% of water is stored in the ocean. It is evaporated, and then precipitated on the land. Some soaks in through infiltration, some flows as streams through runoff, and some evaporated back into the air is used by plants through transpiration, some is also stored in glaciers. Most, however, just returns to the ocean through a stream.
What is runoff?
A stream created by precipitation.
What is infiltration?
When precipitation is absorbed into soil
What increases as stream discharge increases?
Width, depth, and the velocity of the water in the stream
What two parameters are streamflow affected by?
Gradient and discharge
What is streamflow?
The fact that a stream erodes and transports based on its velocity (discharge) and channel shape (gradient)
What is a stream gradient?
If the channel slope is steep, the water will flow faster. The slope of the stream over its length.
Cross section is part of the gradient. Cross-sectional shape determines how much of the stream contacts the water. If more is contacting, there will be more friction, slowing it down.
Which type of stream will move more quickly; a wide and shallow stream, or a pipelike and semicircular stream?
The pipelike, semicircular one because there will be less friction due to the cross-section. Less water contacts the smoother sides.
What is the discharge from a stream? What formula is used to measure it, and what units is it measured in?
The discharge of the stream is the volume of water that flows through the stream cross-section each second.
As discharge increases, all other parameters increase as well.
Discharge = velocity/second x width x depth
Units: m3/s
What three things does a stream do, despite its cross-section and other parameters?
- Erodes
- Transports
- Deposits
What occurs during erosion of stream channels?
Particles in transport cause abrasion, acting as cutting tools to scour channel walls
Potholes are also formed by circular currents of eddies.
How is a pothole formed in a stream (erosional process)
By the circular currents of an eddy.
What are the four transport processes that occur in streams?
- Dissolved transport
- Suspended transport
- Saltation
- Bed load
What is dissolved transport?
When ions in solution from chemical weathering and groundwater are transported through streams
What is suspended transport?
Occurs when sediment remains above the bed and is transported through the water of the stream
What is bed load transportation?
When particles are rolling and sliding on the channel floor
What is saltation transport?
When particles are jumping and skipping, and alternate between being on the channel floor and within the suspended load
What is deposition? What are the two types of channel deposition?
- Channel deposit
- Floodplain deposit
Deposition occurs when a stream can no longer carry its suspended load.
What occurs in a channel deposit?
Sand and gravel deposited in bars
What is a floodplain deposit?
Mud deposited beyond the channel
What does deposition often result in?
Graded bedding - larger particles are depositied before smaller particles
Does a stream cut vertically or horizontally?
Vertically, but its banks cave in by mass wasting to form narrow, v-shaped valleys, with waterfalls and rapids in rough channels.
Are waterfalls and rapids more common in narrow channels, or wide streams (like floodplains)?
Narrow channels
Which is more v-shaped, a narrow stream or a wide stream like a floodplain?
A narrow stream valley
What is a narrow stream valley?
V-shaped by downcutting on a steep gradient as the sides cave in
What is a wide stream valley?
Form on gentle gradients, cut mainly sideways forming floodplains, as the stream shifts back and forth across the valley leaving a thick fill of sediment.
What type of stream valley forms on a steep gradient? What about on a gentle one?
Steep: narrow v-shaped river valley
Gentle: wide floodplain
Stream channel: width < depth
Narrow v-shaped valley
Stream valley: width > depth
Floodplain
How does a wide stream valley form?
It evolves from a narrow stream valley
What are the three drainage patterns that occurs?
- Dendritic
- Radial
- Rectangular
Where does dendritic drainage occur?
On uniform bedrock where channels follow local slopes
Where does radial drainage occur?
On mountains and volcanoes
Where does rectangular drainage occur?
When a stream drains over joints, or a fault system that forms right angles
What is an artificial levee?
A method of flood control.
It is artificial. Built along stream banks to increase the volume that a stream can hold.
What is a flood control dam?
Built to store water, and then let it out slowly. This results in reservoirs which can be used for irrigation, power generation and recreation.
What are the drawbacks of dams?
They don’t typically last for more than 100 years. They flood river valleys, displace wildlife, drown forests, and fill with sediment which reduces their overall holding capacity
Where does a meander form?
On a floodplain
What is a cut bank?
Formed by a meander, where the stream erodes the outside of bends
What is a point bar?
Formed by a meander, deposits on the inside
What is an oxbow lake?
Stream cuts across narrow meander necks at cutoffs. The result of a meander trying to straighten itself out.
What is a delta?
Where a stream enters standing water at its mouth, splitting into distributaries
What does a delta split into?
Distributaries
What is the most effective way for water to infiltrate into the ground?
Steady (and not heavy) rainfall. Heavy rainfall results in a lot of runoff, the meeting of plant needs, and therefore little infiltration.
What is the zone of saturation?
The underwater location where pores between particles are completely filled with water
What is the zone of aeration?
The underwater location where pores are filled mainly with air.
What is the water table?
The water table is the surface separating the zone of saturation (bottom) and the zone of aeration (top). It mimics the ground in terms of elevation (ex. elevates with mountains, and is lowest with valleys).
How slowly does ground water move?
In cm/day - very slowly - depending on the nature of materials
What is porosity? How does it effect groundwater movement?
Porosity is the space between sediments/particles, including fractures and other openings.
Porosity is reduced by pores filling with cement and finer particles (lithification)
What must you have to have permeability?
Porosity
What is permeability?
The connection of pores, the ability to transmit water
What is permeable ground called?
An aquifer
What is impermeable ground called?
An aquitard
How does groundwater flow?
Under gravity, from high to low areas, along, curving paths towards a stream
What is a spring?
A spring is an area where the water table reaches the ground surface, a natural outpouring of water. May be due to a “perched” water table, perched on an aquitard.
What is a hot spring?
Occurs where groundwater is heated by either the geothermal gradient or by cooling magma and then rises to the surface
What is a geyser? Give an example of one; how frequently does it erupt?
A geyser occurs where water is pressurized, and boils, it then vaporizes and blasts water into the air. Usually above a cooling pluton. Water fills the pipe, and this cycle continues. Cyclic events.
Ex. Old Faithful - erupts approximately every hour
What is a well?
A well is a hole drilled into the zone of saturation, past the water table. It must be drilled deep enough to retrieve water during a dry season. A well creates a cone of depression, which occurs when the water table is drawn towards the well
What is a cone of depression?
Occurs where a well drills into the water table, causing the water table to be drawn downward towards the hole.
What is an artesian well?
A well drilled into an aquifer that is sandwiched between two aquitards. Therefore the water is pressurized and rises to the surface easily, with minimal pumping.
What are two environmental problems associated with wells?
- Subsidence
- Ground water contamination
How may a well cause subsidence?
If water is removed for irrigation quicker than it can be replenished, underlying sediment may compact, resulting in gradual sinking of the ground surface
How is contamination an issue with aquifers and the water table?
From septic tanks, fertilizers, toxic spills, and leaking sanitary tanks. Take many years to flush out of an aquifer. Therefore they should only be deposited in impermeable ground areas.
How can contamination of an aquifer be prevented?
By depositing contaminants into impermeable ground (i.e. aquitards)
Why does the leaning tower of Pisa lean?
Due to ground subsidence
How are caverns formed?
Formed below the water table where groundwater dissolves (dissolution) soluble rocks (ex. with carbonic acid). This occurs just below the water table.
What are stalactites and stalagmites?
Needle-like stalactites come down from the ceiling floor by water dripping, stalagmites grow up from the cave floor. Sometimes stalagmites and stalactites join together to form columns.
What is karst topography?
The landscape formed by groundwater dissolving soluble rocks. If cavern ceilings cave-in, they result in sinkholes, into which streams can disappear.
What type of terrain do sinkholes appear in?
In limestone terrain that can be dissolved and collapse to form sinkholes.
What are the two types of glaciers?
- Ice sheets
- Valley glaciers
What is an ice sheet glacier?
A glacier with radial flow. A large ice mass on a continent (ex. Antarctica)
What is a valley glacier?
In a mountain, commonly flows down old stream valleys.
How quickly does a glacier flow?
cm/day is normal
What are the two layers of a glacier?
Upper: brittle (50 m)
Lower: plastic flow
Where does internal flow occur in a glacier?
Below the brittle layer in the plastic layer
What two factors determine the budget of a glacier?
- Accumulation
- Ablation
How does accumulation occur?
By gaining snow or ice
How does ablation occur?
Through wastage or loss by melting, evaporating, or icebergs calving (breaking) in water
What happens if accumulation > ablation?
The glacier’s terminus will advance
What happens if accumulation < ablation?
The glacier’s terminus retreats
Which way does a glacier always move? (even during retreat)
Towards the front
Where is the zone of accumulation? Where is the zone of ablation?
Accumulation: top of hill
Ablation: bottom of hill
What two things are involved in glacier-driven erosion?
- Plucking - glaciers “freeze-on” loose bedrock
- Abrasion - glacier and rock debris scour, scrape, and gouge subglacial floor and sides
What is the result of glacial abrasion?
striations and grooves
What is a glaciated valley? What does it become?
A U-shaped valley; it becomes a fjord - as deep as a mountain is high
What is a cirque?
Rock bowls at the heads of glaciers.
What does the word arete mean?
“Knife-edged” - a knife edged ridge
What is a glacier horn?
Sharp mountain ridges and peaks
Where can a fjord be found?
Along a coastline
Where do horns and aretes form?
On the sides of where a cirque glacier came through
What is glacial drift?
Glacially derived sediment
What are the two types of glacial drift?
Till (stony mud with polished stones and striated stones) and striated drift
When are glacial deposits of glacial drift released?
When a glacier melts
What is till?
Rocks that come in a great variety of particle sizes; directly from glacier ice. Stones tend to appear scratched or polished and faceted from glacial transport.
What is a lateral moraine?
Formed from till along the sides of valley glaciers
What is an end moraine?
Formed from till at the terminus of a glacier, from debris being dumped and bulldozed
What is ground moraine?
Till plastered beneath a glacier
What is a drumlin?
A mound that becomes streamlined under a glacier - the blunt end points up glacier
How is till formed, how is striated drift formed?
Till: directly from glacier ice
Striated drift: deposition by glacial melt-water
What is till comprised of? What is striated drift comprised of?
Till: scratched and polished stones, in a variety of sizes
Striated drift: sand and gravel - provides an excellent source of aggregate to build cities
What provides an excellent source of aggregate to build cities?
Striated drift
What is a kettle?
A depression in the ground left by a piece of a glacier that melted there.